Is it permissible for an intermediary to increase the price of land he is commissioned to sell without the owner's knowledge?

There is no harm in brokerage if the broker and the one who will pay his fee are known, because brokerage is a جعالة (a contract for a stipulated reward for performing a task) for carrying out a work, and it requires an offer and acceptance from both parties. Therefore, the broker must inform the buyer of the price requested by the land owner, inform the owner of what the buyer will pay, and disclose his fee to the one who will pay it to him.